• CFEOM
• ophthalmoplegia
• FEOM
• translocation breakpoint
• extra ocular muscles

A small group of neuromuscular disorders appears to specifically target the innervation and development of the extra ocular muscles, resulting in congenital non-progressive ophthalmoplegia and ptosis. These clinically and genetically heterogeneous disorders are classified as congenital cranial dysinnervation disorders (CCDDs)¹ and include Duane’s syndrome (OMIM 126800 and 604356), Moebius syndrome (OMIM 157900), congenital fibrosis of the extraocular muscles (CFEOM) (OMIM 135700, 602078, and 600638), and congenital ptosis (OMIM 300245 and 178300). The extraocular fibrosis syndromes are congenital ocular motility disorders that arise from dysfunction of the oculomotor, trochlear, and abducens nerves, and/or the muscles they innervate. Each is characterised by a specific form of restrictive paralytic ophthalmoplegia, in most cases associated with ptosis. Individuals with the classic form of congenital fibrosis of the extraocular muscles are born with bilateral ptosis and a restrictive infraductive external ophthalmoplegia, with the inability to raise either eye above the midline. In the vast majority of families, this classical form was mapped to the FEOM1 locus on chromosome 12.^2,3 Besides classical CFEOM1, variant phenotypes have been reported as CFEOM2 and CFEOM3. CFEOM2 is an autosomal recessive CFEOM, marked by a severe limitation of eye movements.⁴ CFEOM3 applies to patients who do not fit the typical CFEOM1 or 2 criteria, owing to clinical variations (table 1). As with CFEOM1, CFEOM3 segregates as an autosomal dominant trait.⁵

Three loci have been reported: FEOM1 on chromosome 12 (CFEOM1, 2, and 3),^6–10FEOM2 on chromosome 11 (CFEOM2),⁴ and FEOM3 on chromosome 16 (CFEOM1 and 3).^5,10,11 CFEOM1, linked to chromosome 12, has recently been found to result from mutations in KIF21A, a member of the kinesin motor proteins superfamily.¹²PHOX2A (ARIX), encoding a homeodomain transcription factor, has been …